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6'x6' wall w/deadmen?

Discussion in 'Landscape Architecture and Design' started by mcclureandson, Sep 28, 2004.

  1. mcclureandson

    mcclureandson LawnSite Member
    Posts: 242

    I could use some advice on a wall. I've got a decent-sized solo maintenance operation (60+ resid/comm accounts) and do 8-10 sod installs per year, half a dozen raised beds etc...but this would be my first retaining wall.

    The proposed wall is 76' long, tapering from a high center of 4-5' to less than 2' at each end. They want to use 6'x6' pressure treated w/deadmen to save on materials/labor associated with block...knowing full well it won't last nearly as long.

    Do the same principles apply for wood walls as stone? I should compact a base, level and bury the first course, backfill with gravel, add drainage etc...? I'm wondering about the spacing of deadmen (this is clay soil, not retaining a severe slope) and any vertical support posts I might need? The wall would look much cleaner, IMO without vertical posts (which seem to turn a retaining wall into a glorified fence) but I would defer to someone with greater experience in this area...

    I'm trying to expand my business to include more landscape work...getting tired of mowing all day, but like to take things slowly and make sure my education and experience are sufficient for each new job. Thanks for any suggestions.
  2. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    I would strongly recommend comparing the cost difference between a SRW and a timber wall. You may be very surprised to find out that there are lots of block products that are very cost competitve with timbers. All wood products are expensive right now. Have you priced a sheet of p/t plywood lately :dizzy:

    Whenever I have requests for timber walls, I ALWAYS try to steer the customer to SRW.

    That said, I've only built them with deadmen going back into the soil, never with vertical supports. Using the same guidelines for a SRW would be beneficial as well. The other factor you should consider is including batter in your construction technique, which means stepping each course back from the one below, about 1" or so.

  3. mcclureandson

    mcclureandson LawnSite Member
    Posts: 242

    Thanks, I am aware of the rising cost of lumber...it's costing me a fortune on my new house! Somehow it didn't come to mind during my walk-through with the customer...regarding batter, same principles apply as with stone? A 6"x6", set back 1" every course will have more pitch into the slope than a stone wall based on a higher number of courses, right? Does batter help that much on such a short wall? Could you set back every other course? Also, is a deadman more beneficial the higher it is set on the wall?
  4. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    Sorry, I didn't pay a lot of attention to the height. But, yes, even with a block wall there can be a fair amount of batter -- all blocks are different. Some faces are near vertical, while others (Allan Block 12 degree for example) set back about 1" each course. 1" may be a little excessive, but remember that timber walls generally have a tendency to lean out. Your batter is not as important on a 2' wall, but you want to keep the look consistent.

    I don't know that I would say the deadman are more beneficial towards the top. In SRW's that require geo-grid, the first layer of grid is set on the bottom course, and generally, every second course thereafter. Don't try to compare geo-grid to deadmen though. Grid runs the entire length of the wall, while a deadman only covers a 6" area. Although tempting, I wouldn't skimp on the deadmen. They are needed throughout the wall to do the job. Remember that deadmen on the bottom will do a lot of work too, as they have more soil surrounding them.

    I'll find a pic of a 4' block wall with 12 degree (1") batter.
  5. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    here is the 12 degree Allan Block on a wall around 4'.

    If you look at the curve on the right hand side of the big stairs, you'll see the batter that equals about 1" per course.

  6. mcclureandson

    mcclureandson LawnSite Member
    Posts: 242

    Thanks for the help...honestly, I'm not trying to get you to build this thing for me! Are there formulas/ratios for length of deadmen, length of 'T' on deadmen, and deadmen spacing in relation to wall height? Sorry for all the questions, I'm just trying to learn theory for different wall types I can apply to later projects...
  7. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Posts: 2,702

    No problem, I just don't have a lot of experience with timber, because I prefer Block.

    I did a search on timber walls. Here's a couple recent threads that might help more.


    I didn't visit this site, but sounds like something that might help:
    Timber Grid - http://www.timbergrid.com/

    Here's a subject appropritate quote from another thread:
  8. D Felix

    D Felix LawnSite Bronze Member
    Posts: 1,898

    Here's another thread that Mark didn't link to:

    There's some good info there.

    Basically as far as spacing, every third course, every 8 feet is what I've always been told/taught. Obviously, for maximum strength, you should alternate the tieback positions, so you don't have a bunch of them stacked on top of each other.

    As for batter, 1/2" per course setback should be adequate.

    The only thing I've done differently with timber walls is to rebar the bottom course of timber into the ground. I'm not sure it does anything structurally, but it helps to keep the timbers from moving around on you while you are building the wall.:)

    Oh, and don't use 12" spikes, get 8" timber screws. You'll need a decent sized drill, but you will save a BUNCH of time, plus they are stronger and the timbers don't move around on you while you are driving the screws...

    Good luck. I'd still rather have a block wall!

    Russ likes this.
  9. mcclureandson

    mcclureandson LawnSite Member
    Posts: 242

    thanks to all...
  10. Lanelle

    Lanelle LawnSite Bronze Member
    Posts: 1,361

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